Wave analyzer



March 29, 1949.

G. W. COOK WAVE ANALYZER FIG. I

Original Filed Jan. 2'7, 1943 9 Sheets-Sheet 1 I SQUARE so EXPONENTIAL PULSES -I v SEC (MI/I 2a LIH PARALLEL OUTPUT INPUT CHANNELS ELECTRONIC swrrcu 6mm WITH BAND-PASS I FILTERS TRIPPING PULSESN I/TIMING Pumas -I I- slac *1" a v.so cvcu-z Fmzousuov COMPENSATING MASTER 1 INPUT SIGNAL OSCILLATOR CATHODE RAY I I I I I OSCILLOGRAPH I sum 1800 Tmms PULSES SAINTOOTH FREQUENCY STAIRWAVE OSCILLATOR AND PHASE OISGILLATOR M N POSITIVE I $0 $50 POSITIVE snwrooru NEGATIVE STAIRWAVE 305195 I-.-I g

(SAWTOOTH) FIG.4

INPUT o 5 soul 600K ouTPuTo-- use 2 mm IOOK INVENTOR.

GEORGE W. COOK LW ATTORNEY SEQRSH ROOM March 29, 1949. G. w. COOK 2,465,355

WAVE ANALYZ ER Original Filed Jan. 27, 15343 9 Sheets-$heet 2 .IztzIIIIIIII \Illl|ll|llllll'llll'lllllllllI l 5 IO I5 20 25 3O POSIHON SCALE f -ALL PASS DUMMY MARKER Eg Q ZER Z E F ERENCE I I I I I I I l I I l I I I I I I I I I I I i I I l I I I OR ZERO REFERENCE INE.

'25 50 I00 200 400 800 I600 3200 s4oo |o,ooo CYCLES PER SECOND 4| FIG. 2

5 40K zuse. .5 u OUTPUT \56 BALANCE ADJUSTMENT 57 FIG. 3

INVEN TOR. GEORGE W. COOK WTIEW G. W. COOK WAVE ANALYZER March 29, 1949.

9 Sheets-Sheet 3 Original Filed Jan. 27, 1945 IOK IOOK

.0055 IOOK;

OUT PUT O'ISOV I NEG.

FIG. 5

2 MEG .1 PEG.

FIG. 6 INVENTOR.

. GEORGE W. COOK R tTTgTRNEY G. W. COOK WAVE ANALYZER March 29, 1949.

9 Sheets-Sheet 4 Original Filed Jan. 2'7, 1943 m um Wm MT m mm FREQUENCY FIG. 7

an A um. ww m Wm wm FREQUENCY FIG. 8

INVENTOR. GEORGE W. COOK BY ATTOR N E Y m MMMCE RGGM March 29, 1949. G. w. COOK 2,465,355

WAVE ANALYZER Original Filed Jan. 27, 1943 9 Sheets-Sheet 5' mmme. 02:11-40 r 5 2 02E 30 O u E March 29, 1949. 5, w, COOK 2,465,355

WAVE ANALY Z ER Original Filed Jan. 27, 1943 9 Sheets-Sheet 6 INPUT FROM :82 O

MASTER OSCILLATOR 3; 500K INPUT FROM 0 I86 SWITCH OUTPUT TO V CATHODE RAY was FIG. I0

255 254 K /6LG esx 2011 500K f gj 304 25s 5 001? |u 0v 00K 500 1:: /30| 253 xix 6547 50K A02 VRI I INVENTOR. FIG. I3 GEORGE w. COOK VBYRW LL20 ATTORPEY G. W. COOK WAVE ANALYZER March 29, 1949.

9 Sheets-Sheet 7 Original Filed Jan. 27, 1943 INVENTOR.

GEORGE w. COOK BY (Shiv KL ATTORNEY March 29, 1949.

G. w. cooK WAVE ANALYZER 9 Sheets-Sheet 8 Original Filed Jan. 27, 1945 N 6E mwwu w 255: r :3 2.

0 OON INVENTOR.

GEORGE W. COOK BY ATTORNEY 04 ON- ouhajzoux PDLE March 29, 1949. G. w. COOK 2,465,355

WAVE ANALYZER Original Filed Jan. 27, 1943 9 Sheets-Sheet 9 l (k 1 o Q .9 L O FIG. l4

FIG. l5

INVENTOR.

GEORGE W. COOK Patented Mar. 29, 1949 WAVE ANALYZER George W. Cook, Washington, D. 0.

Original application January 27, 1943, Serial No. 473,711. Divided and this application February 14, 1945, Serial No. 577,829

(Granted under the act of March 3, 1883, as amended April 30, 1928; 370 0. G. 757) 4 Claims.

This invention is in wave analyzers. As herein described and shown, it is intended to operate in substantially the audio frequencies only, but it will be obvious that in principle it is not thus limited.

The subject matter of the present invention forms a division of my co-pending application Serial Number 473,711 filed January 27, 1943.

In operation, it rapidly resolves and indicates the intensities of sounds simultaneously in a series of selected frequencies originating in a complex sound source. More accurately, its readings, which are proportional to acoustical pressure, must be squared if quantities indicating intensity strictly are desired.

The difiiculties involved in mathematical and mechanical analyses of complex wave forms have stimulated the development of electronic analyzers. The prior art devices, generally speaking, are of two types.

One type involves the use of a single highly selective band-pass filter. A voltage corresponding to the wave form of the sound being studied is heterodyned with a search tone and applied to the filter. An analysis is obtained as the search tone varies in frequency. This type of analyzer iswell known and widely used, but is subject to limitations in speed of analysis and resolving power. One common type requires about ninety seconds to complete an analysis extending continuously through the audible region. It is evident that this type of analyzer is useful only with prolonged, unchanging sounds.

In the second type, a, plurality of filters are arranged in parallel, and the output of each filter is indicated by the height of a corresponding line on the screen of a cathode-ray oscillograph. Connection in turn between each filter and the cathode-ray tube is accomplished up to about ten times a second by a mechanical switch.

\ The present invention is broadly of the second of the above types of instruments. No mechanical switch is used, but by means of a novel electronic switching circuit, the switching rate is increased from about ten to sixty cycles per second. It is to be understood, however, that the novelty of this invention is not limited to the electronic switch, nor to the substitution thereof for a mechanical switch. Neither is the speed of the electronic switch herein illustrated limited to a speed of sixty cycles per second.

This invention is adapted to receive an electric potential, corresponding to the sound under investigation, and apply it to a parallel arrangement of twenty-eight separate filter channels, comprising an all-pass, a, low-pass, a high-pass and twenty-five band-pass filters. The band-pass filters are spaced at intervals of one-th' octave throughout the audio range from twenty-five to ten thousand cycles per second. The output signals of the filter channels are scanned by the electronic switch sixty times per second, and the composite output of the electronic switch is observed as the vertical deflection on a cathode-ray oscillograph.

The analyzer also provides a horizontal deflection voltage for the cathode-ray oscillograph, so as to put on the screen a plot of the distribution of the sound intensity as a function of frequency.

One object of the invention is the provision of a wave analyzer which will substantially instantaneously resolve into pre-selected components a complex wave, and substantially simultaneously produce for visual or photographic inspection the values of all of the components.

Another object is to provide an electronic switching means which will apply to a single line successively and repeatedly and with great rapidity the outputs of a plurality of circuits.

A further object is to provide a stairwave or stepwave generator and means for counting the steps of the generator and resetting the circuit after a predetermined number of steps have been completed.

It is also an object of the invention to use a so-called ring circuit of gas-filled triodes, and to provide means for inhibiting the firing of more than one such tube at a time.

A still further object is the provision of means by which two associated ring circuits may be started and maintained in perfect predetermined time-phase with each other.

It is also an object of the invention to provide with a circuit the output of which is normally a wave form with undesirable voltage peaks means for eliminating the said voltage peaks.

Another object of the invention is the provision of a simple and effective electronic voltage regulator.

Additional objects of the invention will be apparent from a reading of the following specifications and claims.

In the drawings:

Figure l is a block diagram of the analyzer of my invention. The approximate wave forms are indicated beside the pertinent leads.

Figure 2 is a typical pattern such as appears on the screen of the cathode-ray tube.

Figure 3 is a circuit diagram of a typical bandpass filter channel.

H Roeit Figure 4 is a circuit diagram of the low-pass channel.

Figure 5 is a circuit diagram of the high-pass channel.

Figure 6 is a circuit diagram of the all-pass channel.

Figure 7 shows the response curves of the lowpass, the twenty-five band-pass, and the highpass filter channels.

Figure 8 shows the response curve of the allpass channel.

Figure 9 is a diagram of the switching circuits. Figure 10 is a diagram of the output circuit. Figure 11 illustrates the timing circuits. Figure 12 is a diagram of the filter power supply circuit.

Figure 13 is a diagram of the main power supply.

Figure 14 illustrates one form of the electronic voltage regulator of my'invention. Figure 15 shows a modification of the voltage regulator of Figure 14.

GENERAL DESCRIPTION With reference to the block diagram of Figure 1, it is the function of the acoustic analyzer of this invention to receive a signal of complex wave form, to resolve this signal into components falling within definite frequency bands, and to indicate the relative values of these components. The quantity with which the instrument deals is voltage per unit frequency interval, integrated over the respective frequency bands and averaged in some fashion over time.

This is accomplished in the following manner:

A signal obtained from a microphone or other source is applied simultaneously to a parallel arrangement of twenty-eight filter channels. Of these channels, twenty-five contain band-pass filters correspondin to the desired components, one contains a low-pass filter, and one, a highpass filter; the latter two cover components well below twenty-five and well above ten thousand cycles per second. The remaining'channel has an essentially flat frequency characteristic for picking up and averaging sounds over the whole useful range of the analyzer.

Each channel contains an amplifier and a signal rectifier. These, as well as some other elements mentioned in the general description do not appear in the block diagram of Figure 1 as elements. They will be found in subsequent figures and will be described in connection therewith. The output of the rectifier is applied to a condenser and shunt resistance having a time constant of approximately 0.2 second. The voltage appearing across the condenser is proportional to the vector sum of the voltage amplitudes of the components of the input signal lying Within the frequency limits of the associated channel, and this voltage determines the output signal of each filter channel.

By means of a novel switch the output of each of the twenty-eight channels is successively applied sixty time peecond to a common line. There are thirty ste the switch, so that each channel is connected an interval of /1800 second. The two extra steps (there being but twenty-eight channels) are required for synchronization and are normally blank. The common output line leads through another network to the vertical deflecting plates of a cathode-ray tube. The switch is also used to count the steps of a stairwave (also known as-stepwave) generator and to reset this circuit after thirty steps 4 have been completed. The timing of the switch is controlled by a master point pulse oscillator.

The X-axis deflection signal applied to the horizontal deflecting plates of the oscillograph consists of thirty successive increases of voltage, separated by intervals of constant voltage. This sWeep signal is obtained from the stairwave generator, which is controlled by the master oscillator and by the electronic switch. Another signal from the stairwave generator is combined with a sawtooth signal synchronized to the power line frequency and this combination is used to control the frequency of the master oscillator so that it is exactly thirty times the line frequency. A signal from the master oscillator also controls the output circuit and synchronizes it with the switching circuits.

The composite output of the electronic switch is applied to an output circuit before passing to the vertical deflecting plates of the oscillograph. This output circuit modulates the output signal of the electronic switch and controls the final indication on the cathode-ray oscillograph. The timin signal applied to the horizontal deflecting plates of the oscillograph is reproduced on the screen as a series of thirty equally spaced spots, corresponding to the thirty steps of the stairwave. If the output of the switch were applied directly to the vertical deflecting plates of the oscillograph, the screen pattern would consist of thirty spots appearing at various heights above the spots on the axis. The height of the displaced spot in each case would be proportional to the output voltage of the corresponding channel. The output circuit transforms thisthirtystep histogram output of the electronic switch into thirty exponential pulses as shown in Figure 1, extreme upper right hand corner. The height of each exponential pulse is proportional to the signal amplitude of the corresponding channel in the switch output. The pattern on the oscillograph screen then assumes the appearance of a set of thirty vertical lines or thermometers which rise and fall as the output voltages of the corresponding channels change.

Merely because of lack of space, the oscillograph pattern of Figure 1 does not include the full number of thermometers. For the same reason the stairwave form shown does not include thirty steps.

A typical pattern appears in Figure 2, wherein will be seen two horizontal scales below the pattern proper. The upper scale 40 is graduated from 1 to 30, and each marker on the scale represents one of the filter channels, except for the markers at 1 and at 30, which latter are so-called dummy markers, the pattern spots above these indicating the base line above which the heights of the other lines are measured. From a comparison of upper scale 40 with the lower scale 4| (which is similar but is calibrated in cycles per second), it will be seen that marker 2 of scale 40 represents the low-pass filter values; markers 3 through 21, the band-pass channel responses; 28, the high-pass; and 29, the all-pass. The thermometer above marker 29, in other Words, the all-pass indication, has a different vertical scale than the others of the pattern, since otherwise it commonly would be off the screen entirely. The arrangement that makes this possible will be described later in the specification.

It should be understood that Figure 2 is somewhat diagrammatic. In the o'scillographic pattern itself, the background, of course, is dark and the thermometers; appear as streaks of light.

Further, the thermometers are not quite as regular in form as they appear in the drawing.

A standard commercial cathode-ray oscillograph is used to indicate the amplitudes of the to. Where this practice would congest a portion of a drawing unduly, the value may be spaced from the element to which it applies and connected therewith by a dotted line. If a comoutput voltages of the various channels. Minor ponent is repeated in a circuit, the value thereof modifications of the commercial form of the osis given only once. cillograph circuit are necessary to adapt it to FILTER CHANNEL CIRCUITS the type of indication desired in this instrument, but these will be obvious to those skilled in the As prevlously descrlbed, twenty-elem filter m channels are arranged in parallel between the in- The analyzer is designed to operate on 1 put receptacle and the input to the electronic t and 6Q Cyc1e regulated power. A Standard switch. Twenty-five of these channels contain voltage-regulating transformer can be used to Wind-pass filters Whlch have timed frequencies Supply this power f m a Sing1e phase 7 1; differing successively by one-third of an octave. 60 cyC1e1ine TWO power Supplies, each t One channel contains a low-pass filter having a in electronic voltage regulators, provide plate cut-Off t about twenty-five cyclesper second; voltage to the filter channels and to the timing one Contams a hlgh'pass filter havlng a cut-Off circuits, switching circuits, and output circuits at about P thousimd cycle? Per Second; f respectively one contains an amplifier having a response umform within plus or minus five per cent from DETAILED DESCRIPTION about two cycles to thirty thousand cycles per As is apparent from an inspection of the drawsecond. ings and of the brief descriptions thereof, each The table gives the filter components for the figure represents a difierent circuit component particular embodiment of the invention which of the invention. Due to the number and com-- is herein described. It will be obvious that modiplexity of these circuits, it is not possible to show fications of the system, as, for instance, the use in detail in one figure the whole combination; inof difierent frequency bands, will require changes stead, the description and the block diagram in the characteristics of the filter elements.

Table Component Number in Figure 3 46 60 61 56 46 62,63 64 65 66,67 68 69,70 71,72 Frequencies, 0. P. 8.

Unit Value K K. K 9 pf 1 ,uf ,uf I. 141' lf if I] See Figure4 40 10 100 250 0.1000 1.200 0.1900 40 0.2 0.10 0.50 19 40 s 100 100 0.1000 1.200 0.1900 40 0.2 0.10 0.50 12 40 6. 67 100 500 0.1000 0. 600 0.0960 40 0.2 0.10 0.50 15.100 40 8.57 100 500 0.1000 0.600 0.0960 40 0.2 0.10 0.50 9.500 40 6. 67 100 000 0.0500 0.600 0.0060 40 0.1 0.10 0.25 6 40 s e 100 0.0500 0.660 0.0600' 40 0.1 0.10 0.25 6.300 40 s 100 000 0.0500 0.240 0.0380 40 0.1 0.10 0.25 5.940 40 4 m 100 0.0500 0.240 0.0380 20 0.1 0.10 0.10 5.740 40 10 100 166 0.0100 0.180 0.0300 s 0.1 0.01 0.10 3.150 40 s 40 000 0.0100 0.180 0.0300 s 0.1 0.01 0.10 2 40 10 100 000 0.0100 0.120 0.0190 s 0.1 0.01 0.10 2.130 40 6.67 m 0.0100 0.120 0.0190 s 0.1 0.01 0.10 1.344 250 5 23.1 250 0.0010 0.120 0.0196 s 0.1 0.01 0.01 0.646 250 s s 30 0.0010 0.060 0.0096 s 0.1 0.01 0.01 1.065 250 5 28.3 000 0.0010 0.060 0.0096 s 0.1 0.01 0.01 0. 672 250 2.50 7.5 0.0010 0.060 0.0096 s 0.1 0.01 001 0.426 500 s 250 0.0002 0.036 0.0056 s 0.1 0.01 0.01 0.390 500 s a 71.4 0.0002 0.024 0.0038 s 0.1 0.01 0.01 0.369 500 4.75 on 50 0.0002 0.024 0.0038 s 0.1 0.01 0.01 0.262 500 2. 50 200 32.5 0.0002 0.024 0.0038 8 0.1 0.01 0.01 0.146 500 6.67 500 100 50 0.012 0.0019 s 0.1 0.01 0.01 0.184 500 5 s 50 50 0.012 0.0010 s 0.1 0.01 0.01 0.116 500 4 e 50,1 0.012 0.0019 8 0.1 0.01 0.01 0.0732 500 4. 44 m 500 50 0.006 960 s 0.1 0.01 0.01 0.092 500 3.33 m 100 50, 0.006 960 s 0.2 0.01 0.01 0.05:;

See Figure5 See Figureo The values of resistors corresponding to resistor 73 of Figure 3 must be carefully selected to give the filter The values are not listed because the selection requires closer tolerances than those usually implied by the nominal value of a resistance.

1 In this table, as in the drawings, a capacity value, when followed by the notation is in terms of microchannels the desired characteristics.

Inicrofarads.

Consider first the typical band-pass channel of Figure 3, The arrangement of resistance 45 and condenser 46 provides a preliminary filtering action. The signal is then amplified by pentode tube 41 and fed into the filter network.

The output of the filter network is fed through a gain control 48 to the grid of a second amplifier tube 49 and thence to the grid of tube 50. The latter tube uses both plate and cathode coupling to apply a push-pull signal to the plates of a fullwave rectifier 5!. The rectified output voltage appears across resistance 52, condenser 53 and resistance 54. This network has a time constant of 0.2 second (for discharge), and, accordingly,

out. A fraction of the voltage across resistance 54 is applied to the grid of the direct-coupled,

cathode-follower tube 55. The output of the cathode network of this and every other channel is connected to the suppressor grid of a separate matrix tube of the electronic switch (Figure 9) to be later described.

In each filter channel there are four resistance controls. The first, 56, determines the selectivity of the filter and is permanently set in accordance with the values given in the table. Potentiometer 48 also is not normally varied. It is adjusted so that a desired input level to the filters, between 0.1 and 1 volt root-mean-square, yields a voltage at the plate of 5| suitably within the linear range of this type of tube. Potentiometer 54 is the Gain zero adjustment which will be further mentioned later. It controls the signal reaching the grid of tube 55 and ultimately the amplitude observed on the oscillograph screen. The usual adjustment is such that 1 volt R. M. S. (root-mean-square) into each channel produces a, 2-inch deflection. Potentiometer 51, the Balance adjustment, determines the potential of the suppressor grid of the associated matrix tube in the electronic switch. It and the corresponding potentiometers of the other filter circuits are adjusted so that, with no signal, equal displacements, about 0.2 inch for all channels, are observed on the screen. The output signal of a channel is the variation above this initial voltage, and the matrix tube suppressor grid accordingly serves also as a signal grid.

The low-pass, high-pass and all-pass filter channel circuits are shown in Figures 4, 5, and 6, respectively. The high-pass and low-pass channels differ from the band-pass channels only in the filter design. The all-pass channel contains only the last four tubes of a typical channel. These filter channels are fundamentally similar to that of Figure 3, and will not be described in detail. The values of the important components appear on the drawings.

The frequency curves of the filter channels appear in Figure '7. Figure 8 is a separate curve of the all-pass channel response.

SWITCHING CIRCUITS The purpose of the switching circuits is to apply voltage levels proportional to the output voltage levels of the twenty-eight channels to a single line successively and repeatedly. The switching circuits consist of the following fundamental circuits: The fast-switching ring, the inter-ring pulse-generator, the slow-switching ring, the clipping tubes, and the matrix tubes.

The following description refers chiefly to the circuit diagram of the switching circuits in Figure 9. Reference characters and electrical values therefor are given for only a portion of each circuit. Unless otherwise noted, the components and the values thereof are repeated throughout the respective circuits. Tubes in the fast ring are numbered from 86 to 85, inclusive. Tubes in the slow ring are numbered ml] to I84, inclusive.

Fast switching ring Positively-polarized point-pulses, i. e., sharp pulses of voltage which last for only a small fraction of their period of repetition, are delivered from the master pulse oscillator through the condenser |05 at a repetition rate of 1800 per second. These pulses are applied to the grids of all six tubes of the ring through individual blocking condensers, aslflB. The six tubes of the ring are thyratrons (gas-filled triodes) which have such a high negative grid bias that under normal conditions they are non-conducting. Under equilibrium conditions, the positive input pulses are not of sufficient magnitude to fire the tubes.

Consider the situation when one tube is already conducting, say 8|. Current fiowing through this tube raises the potential of the cathode because of the IR drop in resistor lil'l. By IR drop is meant the voltage drop in the resistance due to the passage of current therethrough. Current flows from the cathode of tube 8| through resistors I08 and I09. The IR. drop in resistor 109 reduces the grid bias of tube 82, but not sufficiently, however, to fire 82. The decreased bias voltage is such that the next positive pulse from the master pulse oscillator, second later, will cause 82 to fire. Thus, current through tube 8| primes tube 82, so that the next pulse fires 82 in preference to all other tubes in the ring. While tube BI is conducting, the condenser H0 is positively charged on the right hand side and at ground potential on the left hand side. When tube 82 becomes conducting, the left hand plate of this condenser is suddenly raised to a positive voltage well above ground. This drives the cathode of tube 8| momentarily positive with respect to its plate until the induced charge 011 HO leaks off through resistor I01. Conduction in thyration 8i ceases since its plate is negative with respect to its cathode. On the next pulse, the cycle is repeated with tubes 83 and 82.

Each tube as it becomes conducting extinguishes the preceding tube and primes the next tube. The tube 85 acts on tube 80 in the same inznner as any other tube acts on its succeeding On the basis of the description to this point there could conceivably be established a condition with alternate tubes in the ring conducting simultaneously. That is, 80, 82, and 84 might fire together and prime 8|, 83, and 85 for firing on the next pulse from the master oscillator. When the latter fired, they would first extinguish, then prime, 80, 82, and 84. The cycle would be repeated indefinitely at a rate of 900 per second. Such behavior is inherent in thyratron counting rings with more than four elements. In this switch such a tendency is inhibited in a novel manner by the capacitative coupling l l 5 between the cathodes of tubes 82 and 84. When 82 ignites, an extinguishing pulse is delivered to 8| and 83. In addition, the cathode of 84 is made positive momentarily and this pulse is delivered to the cathodes of 85 and 83 through condensers H6 and I I1, respectively. Thus, if the ring starts out with more than one tube conducting, all tubes except 82 will be extinguished after one cycle of operation of the ring.

The method of self-quenching exhibited by this ring circuit prevents the accidental condition in which two tubes are fired simultaneously'from s ine san Elihu six tubes. If more than one tube fires as a result of these'enhanced pulses, the extra tubes will be extinguished after one cycle of operation of the ring, as previously described.

Inter-ring pulse generator The input for the inter-ring pulse generator is obtained from the cathode of tube 80. When 80 is ignited, 85 is extinguished. The cathode of tube 80 goes highly positive momentarily, then remains at a lower but fixed positive value during the time the tube conducts. The resulting peaked square-wave signal is applied to the grid of thyratron I20 through resistors I2I and I22. I20 is normally non-conducting, but ignites n the peak of the positive signal from the cathode of tube 00. I20, therefore, fires with the same frequency as 80; namely, 300 times per second. A condenser, I23, is in parallel with the tube I20. This condenser charges through the resistance I24. The voltage to which it charges is limited by a diode, I25, which in turn determines the amplitude of the pulse developed across resistor I26. Extinction of tube I20 occurs while tube 80 is still conducting.

Positive point-pulses are thus obtained from the tap on I26. They have a duration of a few microseconds and a frequency of 300 per second.

Slow switching ring The input to the second or slow switching ring consists of the positively-polarized pulses, having a frequency of 300 per second, which are generated by tube I20. These are applied to the grids ofall five thyratrons (I00 to I04, inclusive) in the slow ring through individual condensers, as I21. The tubes are normally non-conducting, and the positive pulses applied to the grids are just great enough to cause any of the tubes to fire. When a given tube is conducting it raises the grid voltage of the succeeding tube by means of the connection between the cathode of one tube and the grid of the following tube, 1. e., resistor I28. Thus, if tube IN is conducting, the grid bias of I02 is reduced to such a point that the next pulse applied to the common input will ignite tube I02 a few microseconds before it has increased sufiiciently to reach the ionization potential of the other tubes. When I02 is fired, a pulse appears on the cathodes of IOI and I03, through the intercathode condensers I29 and I30, respectively. Tube IOI is consequently extinguished, and tube I03 is prevented from firing. In addition, a positive pulse is delivered to the cathode of I04 through condenser I3I. This prevents tube I04 from firing and makes the cathodes of I03 and I00 more positive than they would otherwise be. Thus, although the pulse delivered to the common grid input has sufiicient magnitude to fire any of the five tubes, the tube which is primed actually fires before the other tubes, and conduction of this tube prevents the other tubes ofthe ring from firing.

The priming on tube I 00 is obtained partly from tube I04 and partly from tube 80. Resistor I32, between the cathode of tube I04 and the grid of I00 is larger than the analogous resistors, for example, I28. It is shown as 300 K. instead of 100 K. There is also a lead from the cathode of tube 80 of the fast ring to the grid of thyraton 100 through resistor I33. The firing of tube I04 alone does not fully prime tube I00; the latter will be fully primed when tubes I04 and 80 fire together.

This novel double priming of tube I00 contributes what may be called a selective starting feature to the slow ring for, by this means, the first tube of the slow ring is forced to fire when the first tube of the fast ring fires; this insures perfect time-phasing of the two rings. If, by chance, the firing sequence of the slow ring becomes disorganized, tube I04 will remain fired and will provide a half-priming on tube I00 until the time when tube is fired. Ignition of this tube produces full priming of tube I00 and starts the ring operating again in proper sequence and time-phase with respect to the fast ring. It is because of this positive lock-in between the two rings that a synchronizing signal can be taken from the slow ring to the stairwave generator, and ultimately, to the master oscillator, to keep the entire system in proper sequence and time-phase and in synchronism with the GO-cycle power line.

The selective starting and the waiting until synchronism features of the slow ring, which are provided by the two sources of priming for tube I00 and which permit the perfect synchronism of the two rings, are not essential, because of the positive extinction of other tubes by condensers I3I, I29, etc. They are important, however, adding to the stability of operation of the slow ring and the combined rings.

When tube I00 ignites, the voltage of the cathode becomes positive. A lead is taken from this cathode to the stairway generator. The signal on this lead consists of a positive voltage during the time I00 is conducting. I00 conducts for an interval of second with a frequency of 60 per second. This signal is carried to the stairwave generator of the timing circuits (Figure 11). The action of this pulse will be described later in the section on the Timing circuits. Thus the switching rings act not only as control tubes for the matrix tubes of the switch, but also as a counting circuit. This has the effect of stabilizing and synchronizing the stairwave form to a pattern of exactly thirty steps.

Clipping tubes The term clipping tube is used herein to denote a tube the function of which is to clip" off undesired peaks of a given voltage wave, i. e., the clipping tube operates as a voltage limiter. In its application here, the clipper is used to cut off the sharp peaks caused by the extinguishing action of the cathode coupling condensers; these peaks, in both a positive and a negative direction, are of about twice the magnitude of the switching potential developed at the cathode of the gas triode. Failure to eliminate them causes spurious and undesirable voltage pulses in the output of the electronic switch which tend to confuse its already-complicated composite output signal. The application of this clipping principle to the elmination of the undesirable switching pulses obtained from the ring-counter types of electronic switch is believed to be novel.

One tube, a duplex diode, is used to limit the output signal from each thyratron in the two ring circuits. These clipping tubes by-pass the sharp, high-frequency pulses in the output of the ring tubes and provide a regular square wave. All clipping tubes for the fast ring are connected in the same way; likewise. all clipping tubes for the slow ring are connected in the same way. However, because the maximum output signal voltage of a tube in the fast ring must be negative or zero, while the output voltage of a tube in the slow ring must be positive, the groups of clipping tubes for the two rings are connected differently.

The clipping tubes for the slow-ring thyratrons I to I04, inclusive, are numbered I40 to I44, respectively. Consider as an example the duo-diode I42. The output of thyratron I02 consists of a positive square wave with a sharp positive peak on the leading edge of the square wave and a sharp negative peak on the trailing edge. When a negative voltage is applied to the ring side of tube I42, the cathode I42 is negative \m'th respect to its plate. The lower diode conducts and the negative signal is effectively short-circuited to ground. This limits the output of thyratron I02 to positive voltages.

The operation of the other part of tube I42 is as follows: When the ring side plate is more positive than its cathode I42 the other diode of I42 (1. e., cathode I42 and its associated plate) conducts. The signal voltage is thus limited by the voltage of the cathode I42 of the tube. This cathode voltage is determined by the equilibrium voltage of condenser I45 shunted by resistance I46. This voltage is developed by the continuous flow of current from each clipper tube in succession. Condenser I45 is constantly being charged since one of the five slow-ring clipping tubes is always conducting. It discharges at a constant rate through resistance I46. Consequently the maximum value of the output signal of the ring tube is determined by the value of resistance I46.

.The clipping tubes for the fast ring tubes 80 to 85, inclusive, are numbered I50 to I55, respectively. Now consider tube II. The output of thyratron BI consists of a positive square wave with positive and negative peaks as before. However, the reference voltage of the positive pulse is to be below cathode potential since the entire signal is to be applied to a control grid. Consequently the upper limit of this signal must be little greater than zero voltage. This is accomplished as follows: When plate I5I of duplex diode I5I is positive, the right hand diode of this tube conducts; this eifectively shorts the signal to ground. When cathode I5I of tube I5I is negative with respect to its plate I5I the left hand diode of the tube conducts. Therefore, the output of tube 8| cannot be more positive than the voltage drop in the diode (referred to ground) and cannot be more negative than the plate I5I of tube I5I. The voltage of this plate is fixed by the voltage across condenser I56. This condenser is constantly being charged because one o of the clipping tubes for the fast ring is always conducting. It is constantly being discharged through the shunt I51. Consequently, the reference voltage for the pulses delivered by thyratron 8| is negative and is determined by the resistance I51.

The networks comprising (for example) resistors I60, NH, and I62, in the one case, and I10, I1 I, and I12, in the other, determine the grid bias voltages of the matrix tubes for the slow ring and the fast ring.

Matrix tubes The switch proper consists of thirty pentodes arranged in rows of six tubes each and columns of five. The clipped output of each thyratron in the fast ring is applied to the control grids of all of the five tubes of the corresponding column. The clipped output of each thyratron in the slow ring is applied to the screen-grids of all Of the -12 six tubes of the corresponding row. The matrix tubes are normally non-conducting, since both control and screen grids are biased beyond cutoff.

If tube BI is conducting, however, the control grids of all of the five tubes in the column associated with it are brought above cut-off potential. If thyratron I02 is conducting, the screen grids of all the six tubes in its row are brought above cut-off potential. For a matrix tube to be conducting, both the screen grid and the control grid must be at elevated voltages. Consequently, only pentode I15 is conducting.

The cycle of operations is as follows: Assume that thyratron I00 of the slow ring is conducting. The fast ring goes through its cycle with each of the six tubes conducting in the order 80 to 85. When the fast ring completes its cycle, I00 is extinguished, and IM becomes conducting. The cycle of the fast ring is repeated, and the conducting tube in the slow ring changes again. This continues until all combinations of pairs between the fast and slow rings have been conducting simultaneously. One complete cycle of the switch occurs every ,4 of a second in the apparatus herein shown and described.

The output lead of each of the twenty-eight filter channels is connected to the suppressor grid of one of twenty-eight of the thirty matrix tubes. The two remaining tubes, as I16 and I11, have fixed voltages applied to their grids to provide a reference level for the output signal voltages of the other tubes. These two tubes supply the dummy markers on the oscillograph screen. All

. of the tubes in the switching matrix have a common plate resistor, I 18. The output signal of the switch is taken from this common plate lead to the output circuit, and it is fed to the composite output circuit of the analyzer.

OUTPUT CIRCUIT The output circuit, Figure 10, receives a complex signal from the electronic switch and modifies this signal so that a convenient pattern will be obtained on the cathode-ray tube screen. The input to this circuit consists of a histogram in which the voltage at a given time is proportional to the output voltage of the corresponding filter channel. Each of the thirty matrix tubes of the switch circuit is connected to the input line for an interval of /1800 second at a rate of sixty times per second.

The input signal is applied directly to the grid network, I I 80 I80 of pentode tube I80. During each of the periods of V1800 second the grid voltage is constant and the plate current is constant. Consequently, during each period, condenser I8I is charged. The time constant of this condenser is short compared with A second, so that I8I is practically fully charged after about /3 of this period. The voltage across I8I is essentially equal to the plate voltage of tube I80, which is determined by the current flowing through this tube and resistor I82 and is proportional to the signal grid voltage.

Normally thyratron I83 is not conducting. At the end of each second interval, a positive pulse (obtained from the timing circuit) is delivered to the grid of I83. This pulse ignites I83 and condenser IBI discharges.

The voltage across tube I83 drops almost instantaneously to a value which will not support the discharge, and the tube is extinguished. The charging cycle is then'repeated. Again the final 13 voltage across condenser I8I is determined by the plate current in tube I80.

The voltage across condenser I8I increases exponentially with time to about 9'7 per cent of the charging voltage, then decreases abruptly to zero, then increases exponentially again to about 97 per cent of a dilfel'ent charging voltage, which is determined by the output amplitude of the particular filter channel which is connected to it through the electronic switch. This cycle is repeated indefinitely. This signal is applied to a duplex diode I84. When arranged as shown this tube removes negative peaks introduced into the signal by the action of thyratron I83. The series rectifier will not pass the negative part of the signal. However, due to the inter-electrode capacity of the tube, sharp negative peaks are passed through the rectifien These are shortcircuited to ground by the parallel rectifier.

The diode I85 in the cathode lead of pentode.

I80 serves two purposes. One is to provide a cathode load and introduce degeneration into the operation of tube I80; this could equally well be done by a resistor. Further, small slow changes in the heater voltage of the matrix tubes of the switch, due to supply-line voltage changes, produce corresponding level changes in the voltage of the output signal. Diode I85 has the same heater characteristics as the tubes of the switching matrix. When current through the switch is increased by increased heater voltage, the grid of tube I80 becomes more negative and this tube becomes less conducting. However, there is an increase in conductivity in tube I85 due to the same change in heater voltage which decreases the bias on both control and screen grids of I80, thus compensating for the change as it occurs.

The purpose of triode I86 is to operate as an impedance transformer by means of cathode loading and thus to provide a lower impedance output line to the vertical deflectin plates of the oscillograph. This output tube also isolates the sensitivity control I8! from the effects of varying external loading conditions.

The adjustable resistor I00 has an important function not yet described. It provides what may be termed a movable threshold for the indication on the cathode ray tube screen. Adjustment of this resistor de ermines the grid value at which tube I80 will conduct, and thus the lower limit of the indicating thermometers. It is therefore possible, without disturbing the relative heights of the thermometers, to increase or diminish their overall average height.

TIMING Crscmrs The master pulse oscillator, the stairwave generator, and the synchronizer comprise the timing circuits. A schematic diagram of the timing circuits is shown in Figure 11.

Master pulse oscillator The master pulse oscillator consists of a gasfilled triode I90 arranged as a relaxation oscillator having a frequency of 1800 per second. The tube is normally non-conducting. The condenser I9I in parallel with tube I90 charges in accordance with the time constant which is the product of the capacity of the condenser and the sum of the series plate resistors I92, I93, I94, and I95 as modified by the plate current of the tube 2I6.

When the voltage across I9I reaches a critical value, determined by the grid bias of tube I90,

this tube conducts and discharges the condenser in a few microseconds. During the time that tube I90 is conducting, current flows through its cathode resistance network. When condenser I9I is discharged, tube I90 is extinguished. The instantaneous high current causes a positive pulse to appear on the tap of resistor I96; this is delivered through the blocking condenser I96 to the grid of pentode 203 in the stairwave generator. A positive pulse also appears on the tap of resistor I91 and across resistor I98. These pulses are delivered to the switching and the output circuits respectively.

. The frequency of the master oscillator can be adjusted by varying resistance I93 in its plate circuit. Condenser I 99, between the grid network of thyratron I90 and the negative 2l0-volt source, serves the following purpose: When voltage is first applied to the master oscillator circuit, both plates of I99 are carried to a potential of 210 volts with respect to ground. As I99 charges, current flows from ground through resistors 200 and 20I. Until the condenser is fully charged, the grid of tube I90 is thus more than usually negative. This large negative bias has the effect of increasin the breakdown voltage of the tube, and the amplitude of the first few oscillations thereof is increased. These large initial pulses provide an automatic starting of the switchin ring in the absence of properly primed gas triodes. As long as any gas triode is ionized by this starting procedure, the self-synchronizing action of the ring circuits previously described will, after one or two cycles of operation, cause the rings to adjust themselves to the proper operatin sequence and time phase. The starting action of the first switching ring has been explained in the section describing the switching circuits.

202 is a decoupling condenser which prevents the 1800-cycle pulses from passing onto the positive200-volt line and to other circuits which draw their power from this common source.

stairwave generator The stairwave generator consists of a pentode 203, a thyratron 204, and a vacuum triode 205 and their associated networks. The stairwave generator serves the following two purposes:

(a) It provides a timin signal which is applied to the horizontal deflecting plates of the cathode-ray oscillograph.

(b) It supplies a signal to the synchronizer.

The timing signal consists of thirty equal-voltage increments separated by equal intervals of constant voltage. When applied to the horizontal deflecting plates of the cathode-ray oscillograph this signal produces a horizontal row of thirty equally spaced spots. The motion of the electron beam from one position to another occurs in a few microseconds. The beam is stationary in each position for about /1800 second. After the completion of thirty steps, the cycle is repeated.

The signal supplied to the synchronizer has the same form but is opposite in polarity.

The stairwave is produced by charging condenser 2I0 with thirty equal pulses. At the beginning of the cycle, this condenser is uncharged. Pentode 203 is normally biased beyond cut-off. The master pulse oscillator supplies positive point pulses which have constant amplitude and recur at the rate of 1800 per second. These pulses are taken from thetap on resistor I96 and are applied to the grid of tube 203 through the blocking condenser I96. Each pulse causes the same plate current to flow since the trans-conductance of 203 is independent of plate voltage. This, together with the uniformity of the pulses, insures that equal charges pass through the pentode during each conduction period.

Tube 203 is operated between ground and 100 volts. During each conduction period a measured negative charge is deposited on condenser 2 I 0. The magnitude of the current surges in tube 203 and hence the negative voltage increments across condenser 2|0 are controlled by the reistor I96.

As condenser 2|0 becomes negatively charged the voltage between the plate and cathode of thyratron 204 increases. This tube is normally prevented from firing by the bias voltage supplied by the resistance network 2I I, 2I2. After thirty voltage increments have been impressed on the condenser, a positive pulse is delivered to the grid of tube 204 from the slow switching ring, which also act as a counting circuit, as explained in the section describing the switching circuits. This pulse causes 204 to conduct and the charge on condenser 2!!) passes off therethrough. When the thyratron is extinguished, condenser 2! begins to charge again because of the current pulses through pentode 203. This cycle is repeated indefinitely.

If the potentiometer I96 is set too high, condenser 2I0 will become highly charged before thirty steps have been completed. In this case the cathode of thyratron 204 becomes so negative with respect to the plate and grid that the grid loses control, and the tube conducts before the arrival of the timing pulse from the switch ring. This produces an unstable pattern on the oathode-ray screen. If the value of I96 is set too low, the cathode of the thyratron is not sufiiciently negative after thirty steps to allow conduction in this tube, in spite of the positive pulse delivered to the grid. In this case, condenser 2|0 continues to charge until thirty more steps have been completed or until the cathode of the thyratron is suficiently negative to produce uncontrolled conduction. Various types of multiple and unstable patterns can be caused in this way. A wide range of adjustment is necessary to allow for differences in the characteristics of different master pulse oscillator thyratrons.

While thyratron 204 is conducting, the cathode potential is determined by the IR, drop in the plate lead. Consequently the cathode voltage of this tube at the moment of extinction can be adjusted by varying the resistance 2I3.

The voltage appearing across condenser 2|0 is applied directly to the grid of the vacuum triode 205. A positive stairwave consisting of small voltage increments and a large abrupt decrement is obtained from the plate of this tube and is applied to the horizontal deflecting plates of the cathode-ray oscillograph. A negative stairwave consisting of small voltage decrements and a large increment is obtained from the tap on pctentiometer 2M. This signal is applied to the synchronizer.

Synchronizer The synchronizer consists of a thyratron 2I5, arranged as a controlled relaxation oscillator, and a pentode 2I6 which acts as a mixer. The purpose of this circuit is to control the frequency of the master pulse oscillator. It provides a fixed phase relation between the horizontal axis sweep 16: signal on the oscillograph and the power line voltage. To accomplish these ends, the frequency of the master pulse oscillator is adjusted to equal thirty times the instantaneous frequency of the power line.

The relaxation oscillator 2I5 has a free-running frequency of about fifty-five cycles per second. A 3-volt (SO-cycle sine wave is superimposed on the fixed bias of this tube. Although the average frequency of this signal is usually accurately 60 cycles, the instantaneous frequency may diifer from this value. The 3-volt signal on the grid of the thyratron increases the frequency of oscillation of this tube from its free-running value of fifty-five cycles per second to the line frequency. A saw-tooth wave form, caused by the slow charging and rapid discharging of condenser 2I'I, is applied to the screen grid of pentode 2I6. The time constant of this condenser chargin through resistor 2I8 is of the same order of magnitude as the period of the line voltage. Consequently the voltage across condenser 2I'I increases at a nearly constant rate until thyratron 2I5 breaks down. The voltage to which the condenser charges is determined by the time at which the thyratron begins to conduct.

The negative stairwave signal obtained from the stairwave generator is applied to the control grid of the pentode 2 I6. The step structure in the wave form of this signal may in this case be neglected. Essentially this voltage increases in a negative sense linearly with time to a fixed Value, falls abruptly to zero, then increases again. For a given setting of resistances I96 and 2 I 3, the peak negative voltage of this signal is fixed. The rate at which this peak voltage is attained is determined by the frequency of the master pulse oscillator. Adjustment of potentiometer 2! controls the amplitude of this signal.

The negative stairwave voltage from potentiometer 2M returns to zero about three step units /1800 second) before the positive voltage from thyratron 2I5 does. Consequently the two grid voltages effectively combine to produce a current surge in pentode 2I6 near the end of the cycle. This increases the IR. drop in the resistance network I92, I93, I94, decreases the plate voltage of tube I90, and consequently decreases the frequency of the pulses from the master pulse oscillator until the positive voltage on the screen grid of pentode 2l'6 falls to zero. This pentode does not conduct except for this short interval at the end of each cycle; the length of time during which it conducts is determined by the relative phase of the positive saw-tooth signal on the screen grid and the negative stairwave signal on the control grid. If the peak of the negative signal and the drop to zero occur too soon the pentode conducts for a longer period than the normal time of 3 second. This reduces the frequency of thyratron I90 and consequently brings the peak of the negative signal into the proper phase with the positive signal. If the peak of the negative signal occurs too late, the length of the pulse delivered by pentode 2I6 through resistors I92, I93, and I 94 is decreased and compensation and synchronization are obtained.

POWER SUPPLY Two independent electronically regulated power supplies are provided. One circuit supplies voltage for the twenty-eight channels. This is illustrated in Figure 12. The other circuit (Figure 13) supplies voltage for the timing circuits, the switch, and the output circuit.

Filter channel power supply The input voltage to the power pack consists of 120-volt (SO-cycle alternating current regulated by a constant voltage transformer. The transformer is preferably of large capacity, as 2- kilovolt-amperes. While such capacity is not necessary for the operation of the analyzer alone, it is a convenience in view of the fact that auxiliary equipment will commonly be employed. A full-wave rectifier 220 supplies positive voltage for the system. The rectified voltage is pased through a smoothing filter, comprising inductances 221 and 222, and condensers 223 and 224.

The operation of this circuit is as follows: A decrease in the value of the positive input voltage causes the screen grid of pentode 225 to become less positive. This decreases the plate current through the tube and decreases the IR drop through the resistance 226.

Two beam-pentode tubes, 221, and 228, are arranged in parallel and the grids of these tubes are tied to the plate of tube 225. Hence, when the plate current of 225 drops, the plate resistance of tubes 221 and 228 decreases, thus compensating for the original decrease in input voltage.

If the voltage on the screen grid of amplifier 225 were controlled by the resistances 229 and 230 alone, the variations of plate resistance of tubes 221 and 228 would overcompensate the input voltage variations. To eliminate this effect, the screen grid of the amplifier is connected to the cathodes of 221 and 228, through resistance 23!. 23| is tied to the resistance network 229, 230 at a point having the same voltage as these cathodes. Thus, there is no D. C. voltage drop across resistance 23L The excess signal voltage on the cathodes of 221, 228, caused by overcompensation tends to increase the voltage of the screen grid of the pentode 225 because of signal curent through resistances 230 and 231. This adjusts for the overcompensation. The value of 23I is chosen to obtain exact compensation.

Sudden variations in the output load operate in a similar manner on the control grid of 225 through condenser 232. If the load is momentarily increased, a negative pulse is delivered to the control grid. This decreases the plate current of the pentode and decreases the grid bias voltage of the regulator tubes 221, 2 28, thus decreasing the plate resistance of the latter. Condenser 232 also prevents high frequency tube noise from the amplifier tube 225 or the voltage regulating tube 235 from appearing in the output. The nominal output potential of the regulator depends upon the grid bias of the pentode 225, and this is controlled by resistor 236.

Tube 235 has a characteristic such that the voltage drop across it is nearly independent of the current through it. This fixes the voltage of the cathode of pentode 225. In the circuit described and shown it is fixed at 105 volts above ground. Resistance 231 insures sufficient current through regulator 235 to maintain that tube on the stable portion of its operating characteristic.

The negative voltage for grid-bias supply is obtained from a full wave rectifier 238. Two voltage-regulating tubes 23,9 and 240 insure the stability of this voltage supply. Two leads, each at -150 volts, are used to supply the output network in each filter channel.

Three additional electronic voltage regulators, identified in their entireties as 24l, 242, and 243, and identical in operation with the regulator above 18 described are connected in parallel with the first mentioned regulator. The one voltage regulator tube 235 serves all of these circuits.

Main power supply The main power supply furnishes operating power for all units of the assembly with the exception of the filter channels and the cathode-ray oscillograph. It contains two full wave rectifiers, 250, and 25], one half-wave rectifier, 252, and three electronic voltage regulators. A positive ZOO-volt line is regulated by a circuit which includes tubes 253 and 254 and which functions in the same manner as the electronic regulator in the filter power supply. The bias on the screen grid of amplifier 253 is fixed by the resistance network 255, 256, and 251. And the resistance 258, in order to satisfy the condition that no direct current flow therethrough, is tied between resistors 255 and 256 at a point such that its potential is equal to the average potential of the cathode of tube 254. Resistor 258 is adjustable in order that the proper degree of compensation may be obtained.

A second electronic regulator, including tubes 260 and 26!, supplies the positive 110-volt line. The cathode of the amplifier tube, 26! in this case, is grounded directly. Voltage regulator tubes 262 and 263 are provided, and these operate (for the apparatus described) between ground and 210 volts. Between these tubes, at a point of 105 volts potential, a lead is taken, and this lead supplies the reference voltage for the electronic regulator, and, by means of the resistance networks 264, 265, 266, and 261,268, 269, the grid biases for the tubes.

A third electronic regulator, identical with the one just described, comprises tubes 210 and 2H and associated elements; this supplies a negative -volt source. The reference voltage for this current is 210 volts, and is obtained from the negative side of the voltage regulator tube 263.

These two circuits are the same as those already described except for minor difierences occasioned by the different positions of the voltage regulator tubes in the circuits. The current through these tubes is obtained from the halfwave rectifier 252. Tubes 262 and 263 stabilize the negative side of this half-wave rectifier at -210 Volts. The load variations on this grid supply line are not suflicient to require the use of an electronic voltage regulation.

The 3-vo1t A. C. signal used in the timing circuits is taken between one side of the 6.3-volt filament lead and ground.

VOLTAGE REGULATORS In Figures 14 and 15 are shown electronic voltage regulators of my invention. The regulators of the two figures are similar, and both are somewhat like the regulators shown in Figures 12 and 13 and already described. There are important differences however,

Like the regulator of Figure 12, that of Figure 14 comprises a voltage dividin network, consisting of resistors 210, 21!, 212, and 213, across the supply lines, and an amplifying pentode 214 the screen grid of which is varied in accordance with changes in input potential. A rise in screen grid potential. due to an increase in input, increases the current through the tube, and thereby enlarges the potential drop across its plate-load resistor 215. This action adds to the negative grid potential of the series-regulator tube 216, in-

ltislit int.

creasing the plate resistance. This operation controls the output potential of the regulator for changes in input potential.

Compensation of output potential for shorttime and long-time variations in effective load resistance also is provided for in novel manner. As explained in connection with the regulator of Figure 12, any short-time variation in load current is impressed on the control rid of amplifier 214 through the network including resistors 211, 218, 219 and condenser 28!]. 218 serves to determine the nominal output of the regulator. Shorttime changes in load current cause potential changes which are coupled to the control grid of pentode 214 through condenser 280 and which are then compensated for as already described.

Any change in load current continuing for a pefiod longer than that for which condenser 280 can maintain the change at the grid of the amplifier 214 will develop a change in potential across resistor 28!, through which the plate current of the tube 214 and all load current passes. A change of this potential drop varies the cathode-to control grid potential of tube 214 in the proper phase to oppose any change in the output potential of the regulator.

The magnitude of the potential drop across 28! is determined by adjustment of the resistance, and the value of resistance 28l at which neither overcompensation nor undercompensation will occur with changes in load current may be readily ascertained.

A gas-filled regulator tube 282 is used to raise the potential of the cathode of amplifier 214 with respect to ground potential. Since fluctuations of the operating potential of 282 will vary the grid-cathode potential of the regulator amplifier and therefore the output of the system, the selection of the tube 282 should take into account the ability of the tube to maintain its own operating potential. It has been found that a type VR- -105/30 tube is to be preferred to a type CD-2005 in this connection. A battery may be substituted for the gas-filled tube, and will eliminate shorttime fluctuations, but may introduce slow changes in the output due to the charging efiect of the cathode current of the pentode 214.

In determining the point of connection of the screen grid of pentode 214 to the voltage dividing network 210, 21 I, 212, 213, it is necessary, in addition to obtaining the proper operating potential '-for the screen grid, to allow enough of the input fluctuation to appear on the screen grid that the regulator actually overcompensates therefor, before the resistance 283 is inserted in the circuit. A fall in input potential will, in other words, produce a slight rise in output potential.

After proportioning the resistance network so that the screen grid overcompensates for input variations, all traces of overcompensation are removed by the insertion and proper adjustment of the variable resistance 283. Resistance 283 must not carry any load current, and, to this end, it is positioned in the circuit so that points 284 and 285 are at the same average potential. Only voltage changes will then appear across resistor 283. This resistor, in series with the load resistance, and' with point 285 maintained at output potential, forms a shunt for screen-signal potential across the lower portion of the voltage divider network comprising resistors 211, 212, and 213 in series. By adjustment of 283, the voltage change appearing at point 284, and therefore on the screen grid of pentode 214, may be attenuated. It is clear, then, that for some particular value of resistance 283, there will be no change in output due to changes in input. By proper adjustment of this variable resistance, therefore, changes in the plate resistance of tube 218 are caused to compensate exactly for changes in input voltage.

For some applications of the voltage regulator, compensation for long-time voltage variations may be of no importance. In such cases, variable resistor 28l may be omitted, as in Figures 12 and 13, and the regulator will then compensate only for supply potential variations and short-time load variations. It will still maintain the output reasonably constant for long-time variations, but the output can be expected to vary slightly with long-time load changes of the order of twenty per cent. Capacity 280 and resistor 284 should be retained, not only to provide short-time load compensation but to eliminate the fluctuations produced by the regulator tube 282, as already described.

The normal operating current of the screen grid of pentode 214 is drawn from the input through the voltage-divider network of resistances 218, 21L 212 and 213 in series. Any input variation will cause a change in the screen-grid current which will produce a potential drop across 210 and 211 in series tending to oppose the regulating action of the change in screen-grid potential. It is advisable, therefore, to keep the current in this bleeder network as high as possible, so that the degenerative effect of the change in screen current will remain at a minimum. With a two milliampere current, the regulator retains control over the circuit at full load with input variations of plus-or-minus forty per cent; with a one milliampere current, plus-or-minus twenty per cent.

In Figure 15 is shown a modified voltage regulator adapted for higher output potentials than the regulators described. As the output potential is increased, it becomes more important that the electrodes of the regulator amplifier, 290 in Figure 15, be operated as nearly as possible to the output potential. And it is then necessary properly to couple to the control electrodes input and output potential changes. The cathode of the amplifier may be operated at a higher potential from ground by using two tubes in series in place of the single voltage-regulator tube 2!. This will, however, increase the difficulties growing out of the small, short-time fluctuations characteristic of gas-filled voltage-regulator tubes. A more desirable method is illustrated in Figure 15. The regulator-amplifier cathode-tosuppressor connection shown in Figure 14 is eliminated, and the suppressor grid of the tube is connected to the voltage-divider network 282, 293, 294, 295, as at 296. This connection allows the suppressor grid to exert some regulating action in conjunction with the screen grid when the attenuation ratio,

R294+R295/R292+R293+R294+R295 becomes so great--due to the necessity for operating the screen grid at its proper potential with respect to the cathode at high output valuesthat the amplification of the screen grid alone is not sufficiently high to control the plate current of the tube for proper regulation. The resistance network should be so designed that the potential at point 296 is essentially the same as that of the cathode of the amplifier 290.

OPERATION The analyzer is designed to operate on -vo1t 60-cycle regulated power. It draws about 9 amperes at this voltage. The power factor of the analyzer is about 0.99.

Power is distributed to the various elements of the invention in accordance with the diagrammatic circuit drawings herein through any convenient arrangement of junction boxes; and connection is made to an oscillograph.

The voltage level of the input to the analyzer should be of the order of 0.1 to 1.0 volt. An

attenuator or voltage divider should be provided in order to maintain the input signal voltage at this level.

The voltage supplies should be carefully adjusted to their proper values. Some convenient meters, as 300, 30!, 302, and 303 (Figure 13) should be provided for this purpose. The meters illustrated indicate respectively the A. C. line voltage, l20-volts, the positive ZOO-volt plate supply, the positive 110-volt plate supply, and the negative 100-volt grid bias supply. The positive ZOO-volt, positive 110-volt and negative 100- volt supplies can be controlled and adjusted by the variable resistors 304, 268 and 305, respectively.

Six adjustments are provided for use in securing the proper pattern on the oscillograph screen. These may be conveniently termed Zero, Gain, Synchronizer, Phase, Frequency and Stabilizer: and they correspond respectively to the variable or adjustable resistors Hill and I8! (Figure 10), and 2l4, 2|3, I93, and I96 (Figure 11).

The following procedure is suggested for setting up the pattern: all pattern controls are set at minimum, except Zero control which is at maximum. The intensity and. focus of the oscillograph are fixed at convenient levels; the frequency switch of this instrument is turned off; the Y-axis amplifier is at zero, and the X- axis amplifier is at 30.

With the power turned on, the X and Y position controls of the oscillograph are adjusted until a spot appears on the screen. This spot will repeatedly move horizontally across the screen. Adjustment of the Stabilizer control will produce a pattern of thirty spots in a horizontal line. Increase Gain until vertical lines appear, one above each of the thirty spots, to a convenient height, from one to three inches.

Preferably the Stabilizer setting is decreased until the pattern becomes unstable; and stability is reobtained by adjustment of the Synchronizer. This procedure is desirable, because otherwise the pattern may become stable with the line or thermometer at position 1 displaced from its proper position.

Adjust Frequency if any ripple appears in the pattern; and adjust Phase for maximum stability.

Decrease Zero until the right and left hand thermometers are just visible above the horizontal axis. The intermediate thermometers will in general have irregular heights. All controls except Gain are now correctly set. Minor adjustment of Frequency may be necessary occasionally if the pattern develops a ripple, i. e., a slight recurrent shifting of the entire pattern across the screen of the oscillograph, which may be caused by spurious magnetic deflection of the electron beam when the frequency of the electronic switch differs slightly from that of the power-supply line.

Two controls for each filter channel are provided. These may be conveniently termed Balance and Gain zero, and they are respectively the resistors 51 and 54 of the filter circuits (see Figure 3).

Increase Gain until the right and left hand thermometers are about 2 inches high. With no signal on the analyzer input, adjust the twenty-eight Balance adjustments, in order of increasing frequency, until the twenty-eight intermediate thermometers have equal heights. The level of the two end thermometers is the zero signal level. While this adjustment is being made, all of the individual Gain zero controls should be at zero. It should be noted that this adjustment is made at a high Gain setting. As a consequence a certain amount of fluctuation may occur in the height of the thermometers. This fluctuation may, in general, be disregarded. It should also be noted that the heights of the individual thermometers will vary slowly with time as the instrument warms up. To minimize go this and similar effects, it is suggested that the analyzer be turned on at least an hour before accurate settings or measurements are made. After this adjustment has been made, return Gain to a standard setting.

Arrange a beat-frequency oscillator on the input of the analyzer in such a way that a signal of constant voltage and adjustable frequency can be applied to the instrument; the use of a vacuum-tube voltmeter across the input of the analyzer is suggested. Set the oscillator low-pass thermometer rises to 2 inches.

ard deflection of approximately 2 /2 inches.

The same general procedure should be followed for each of the tuned channels; namely, set the oscillator for the lower frequency of maximum response for the channel, adjust the oscillator voltage to the standard value (0.1 volt, R. M. S.) and adjust the Gain zero control for the channel in question to obtain standard deflection of the corresponding thermometer. It should be noted that there is a small drop in response at the center of the frequency-response curve of each filter channel. The lower frequency of maximum response for each filter channel should be used for this adjustment.

The all-pass channel Gain zero control should be adjusted in the same way except that a larger input voltage (0.2 or 0.4 volt) should be used in order to provide a condensed scale for the all-pass thermometer. The displacement of the all-pass thermometer is proportional to the sum of the displacements of the other thermometers.

In adjusting the Gain zero controls, care should be exercised not to disturb the Balance controls of the various channels. After the Gain zero adjustments have been made, the Gain and Gain zero controls should not be disturbed.

The above description is specifically directed to the structure of the drawings. Many changes within the spirit of the invention will be obvious to those skilled in the art, however, and it is to be understood that the invention is not restricted in scope to the embodiment described and shown, but includes everything that properly falls within the appended claims.

The invention herein described may be manu- 

